High gain low distortion bridge amplifier with feedback

Abstract

A bridge amplifier circuit comprising two amplifiers in bridge configuration having a feedback path from the output of one of the amplifiers to the reference input of the other amplifier, together with compensation means for reducing the voltage variation at the reference input. In this way offset and distortion are reduced, although the gain of the amplifier circuit is not affected by the presence of the feedback path.

I claim: 
     
       1. A bridge amplifier circuit comprising: a first and a second amplifier, each having a signal input, a reference input and an output, for supplying an amplified input signal to a load coupled between the outputs, characterized in that a feedback path is present from the output of the first amplifier to the reference input of the second amplifier and that compensation means are coupled to said reference input of the second amplifier for reducing signal variations caused by an output signal of the first amplifier at the reference input of the second amplifier. 
     
     
       2. A bridge amplifier circuit comprising: a first and a second amplifier, each having a signal inputs, a reference input and an output, for supplying an amplified input signal to a load coupled between the outputs,   a feedback path between the output of the first amplifier and the reference input of the second amplifier,   compensation means for reducing signal variations at the reference input of the second amplifier, and   the feedback path comprises an impedance and the compensation means comprise a current source having a current value proportional to the input signal.   
     
     
       3. The bridge amplifier circuit of claim 2, wherein the product of impedance value of the impedance and current value of the current source are chosen so as to provide a voltage at the reference input of the second amplifier for substantially compensating a signal voltage supplied to said reference input by the output of the first amplifier. 
     
     
       4. The bridge amplifier circuit of claim 1, wherein the gain of the first amplifier is higher than the gain of the second amplifier. 
     
     
       5. The bridge amplifier circuit of claim 2, wherein the gain of the first amplifier is higher than the gain of the second amplifier. 
     
     
       6. The bridge amplifier circuit of claim 3, wherein the gain of the first amplifier is higher than the gain of the second amplifier. 
     
     
       7. The bridge amplifier circuit as claimed in claim 1 wherein the gain of the first amplifier and the gain of the second amplifier have mutually opposite polarity. 
     
     
       8. The bridge amplifier circuit as claimed in claim 1 wherein said first and second amplifiers each comprise an operational amplifier with a respective feedback resistor, and further comprising; a reference voltage source coupled to the reference input of the first amplifier, and   first and second signal current sources coupled to the signal inputs of the first and second amplifiers, respectively, wherein   the feedback path includes an impedance and the compensation means comprise a further current source coupled to the reference input of the second amplifier.   
     
     
       9. The bridge amplifier circuit as claimed in claim 8 wherein the first and second signal current sources are proportional to the input signal but of mutually opposite polarity, and the first signal current source has the same polarity as the further current source.   
     
     
       10. The bridge amplifier circuit as claimed in claim 8 wherein the product of the feedback path impedance and the current of the further current source is substantially equal to the product of the impedance value of the feedback resistor of the first operational amplifier and the current of the first signal current source. 
     
     
       11. The bridge amplifier circuit as claimed in claim 10 wherein the product of the impedance value of the feedback resistor of the second operational amplifier and the current of the second signal current source is less than the product of the impedance value of the feedback resistor of the first operational amplifier and the current value of the first signal current source. 
     
     
       12. A bridge amplifier circuit comprising: a first and a second amplifier, each having a signal input, a reference input and an output, for supplying an amplified input signal to a load coupled between the outputs of the first and second amplifiers,   a feedback path coupled between the output of the first amplifier and the reference input of the second amplifier, and   compensation means coupled to the reference input of the second amplifier for deriving a signal voltage at the reference input of the second amplifier proportional in magnitude but opposite in polarity to a signal voltage supplied by the output of the first amplifier thereby to reduce signal variations at the reference input of the second amplifier.   
     
     
       13. The bridge amplifier circuit as claimed in claim 12 wherein the reference input of the first amplifier is coupled to a source of reference voltage, and   the compensation means comprise a current source supplying a current proportional to an input signal applied to the signal input of at least one of said first and second amplifiers.   
     
     
       14. The bridge amplifier circuit as claimed in claim 12 wherein the feedback path comprises an impedance and the compensation means comprise a current source coupled between the reference input of the second amplifier and a point of reference voltage, and the product of the impedance value of the feedback path impedance and the current supplied by the current source produce a voltage at the reference input of the second amplifier which compensates a signal voltage supplied to said second amplifier reference input by the output of the first amplifier and via said feedback path.   
     
     
       15. The bridge amplifier circuit as claimed in claim 13 wherein the gain of the first amplifier is higher than the gain of the second amplifier.